Radiographic inspection apparatus and radiographic inspection method

ABSTRACT

A radiographic inspection method of irradiating a circuit forming device with X-rays to inspect the inside of the device. The method includes an X-ray irradiation step of irradiating the circuit forming device with X-rays, an X-ray detection step of detecting X-rays having penetrated the circuit forming device which is rotated every predetermined degrees of angle about an axis intersecting the irradiation direction of X-rays at right angles, a tomogram creating step of creating a plurality of tomograms based on data on penetrated X-rays detected in the X-ray detection step, a projected image creating step of creating projected images in three axial directions intersecting at right angles based on the plurality of tomograms created in the tomogram creating step, and a defect detecting step of detecting a defect such as a crack of the circuit forming device based on the projected images created in the projected image creating step.

FIELD OF THE INVENTION

The present invention relates to a radiographic inspection apparatus anda radiographic inspection method for inspecting a joint state inside acomponent mounted on a circuit forming device, to be specific a printedboard, and a component packaged with resin or metal, or a joint state ofa component mounted inside a printed board.

BACKGROUND OF THE INVENTION

Conventionally, methods for detecting a defect in a circuit formingdevice such as a printed board with radiation or X-rays for example,include a method of detection from an image obtained by two-dimensionalimage processing on an X-ray transparent image in one direction of acircuit forming device, or a method of detection from an image obtainedby two-dimensional image processing performed separately on X-raytransparent images in two directions and three directions.

In such detection methods, however, the inside of a circuit formingdevice can be viewed only in a two-dimensional manner. Thus a defectcannot be correctly located, a blind spot appears in somethree-dimensional shapes of the circuit forming device, or inspectionsare difficult in some regions, so that accurate detection of a defectcannot be expected.

In order to address the problem, a method using X-ray tomosynthesis(hereinafter, referred to as X-ray CT) is proposed. In this method, aplurality of consecutive tomograms are generated, a defective regionconsidered to be within the range of predetermined threshold valuesrelative to each tomographic plane are binarized and detected, and theregion is numbered, so that the position of a defect, the size of acuboid circumscribing the defect, and so on are measured (For example,Japanese Patent Laid-Open No. 1-297772, page 5, FIG. 3).

In a device for inspecting a defective foreign matter using this method,consecutive tomogram data created by X-ray CT is binarized for eachtomogram based on a predetermined threshold value and regions arenumbered, so that the position of a defect, the size of a cuboidcircumscribing the defect, and so on are measured.

However, in the conventional device for inspecting a defective foreignmatter, a long defect such as a crack intersecting a tomographic planeat right angles is reduced in size on the display and thus becomes hardto extract, and processing on a large number of tomographic planesresults in a longer inspection time.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a radiographicinspection apparatus and a radiographic inspection method so that even along defect such as a crack intersecting a tomographic plane at rightangles can be easily extracted with radiation and a test can beconducted in a short time.

In order to attain the object, a first invention is a radiographicinspection apparatus for irradiating an inspected object to inspect theinside of the object. The radiographic inspection apparatus comprises aholder for holding the inspected object, and rotating the object everypredetermined degrees of angle about an axis intersecting an irradiationdirection at right angles or swinging the object every predetermineddegrees of angle about an axis placed in parallel with the irradiationdirection, an irradiation device for irradiating the inspected objectwhich is held by the holder and moved every predetermined degrees ofangle, a radiation detector for detecting a radiation having penetratedthe inspected object, a data storage device for storing data on thepenetrated radiation detected by the radiation detector, a tomogramcreating device for creating a plurality of tomograms based on thepenetrated radiation data stored in the data storage device, a projectedimage creator for creating projected images in a plurality of directionsbased on the plurality of tomograms created by the tomogram creatingdevice, and a defect detector for detecting a defect of the inspectedobject based on the plurality of projected images created by theprojected image creator.

According to a second invention, the projected images created by theprojected image creator of the radiographic-inspection apparatus arecreated for each of a plurality of projected planes intersecting atright angles.

According to a third invention, the projected image creator of theradiological inspection apparatus creates the projected images bysetting a threshold value for the tomograms to extract therefrom partscorresponding to the defect, and adding the parts corresponding to thedefect extracted based on the threshold value.

According to a fourth invention, the radiation used in the radiologicalinspection apparatus is one of an X-ray, a gamma ray, and a neutron ray.

A fifth invention is a radiographic inspection method of irradiating aninspected object to inspect the inside of the object. The radiographicinspection method comprises a radiation detection step of irradiatingthe inspected object and detecting a radiation having penetrated theobject, the inspected object being rotated every predetermined degreesof angle about an axis intersecting an irradiation direction at rightangles or the inspected object being swung every predetermined degreesof angle about an axis placed in parallel with the irradiationdirection, a tomogram creating step of creating a plurality of tomogramsbased on data on the penetrated radiation, the radiation being detectedin the radiation detection step, a projected image creating step ofcreating projected images in a plurality of directions based on theplurality of tomograms created in the tomogram creating step, and adefect detecting step of detecting a defect of the inspected objectbased on the projected images created in the projected image creatingstep.

According to a sixth invention, the radiation used in the radiologicalinspection method is one of an X-ray, a gamma ray, and a neutron ray.

According to the radiological inspection apparatus and the radiologicalinspection method, an inspected object is rotated or swung everypredetermined degrees of angle, a plurality of tomograms are createdusing data on penetrated radiations such as an X-ray, a gamma ray, or aneutron ray on each moving position, projected images are created basedon the tomograms in a plurality of directions, such as in threedirections intersecting at right angles, and a defect is detected basedon the projected images. Thus, based on the plurality of projectedimages, even a long defect such as a crack can be easily and positivelydetected in any direction.

Numerous characteristics and advantages of the present invention will beapparent from a preferred embodiment described in accordance with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing the configuration of aradiographic inspection apparatus according to an embodiment of thepresent invention;

FIG. 2 is a flowchart for explaining the radiographic inspecting methodaccording to the embodiment of the present invention;

FIG. 3A is a side view showing a case where the radiographic inspectionmethod is used for inspecting a circuit forming device;

FIG. 3B is a horizontal sectional view showing a case where theradiographic inspection method is used for inspecting the circuitforming device;

FIG. 4A is a projected view showing a case where the radiographicinspection method is used for inspecting a circuit forming device;

FIG. 4B is a projected view showing a case where the radiographicinspection method is used for inspecting the circuit forming device;

FIG. 4C is a projected view showing that the radiographic inspectionmethod is used for inspecting the circuit forming device;

FIG. 5 is a projected view showing a variation of the radiographicinspection method;

FIG. 6 is a plan view schematically showing a variation of a holder inthe radiographic inspection apparatus; and

FIG. 7 illustrates operations of the holder in the variation.

DESCRIPTION OF THE EMBODIMENT

The following will describe a radiographic inspection apparatus and aradiographic inspection method according to preferable embodiments ofthe present invention with reference to the accompanying drawings.

In the present invention, an inspection is performed using transparentimages by radiation. In the specific embodiment, X-rays are used as theradiation.

In the present embodiment, an inspected object is a circuit formingdevice. To be specific, the inspected object is a printed board or anelectronic component, or the combined or joined printed board and theelectronic component. The printed board is applied to a single-sidedsubstrate of paper phenol, a glass epoxy substrate with multiple layers,a film substrate, a substrate including an electronic component, andresin on which a circuit pattern is formed.

First, an X-ray inspection apparatus will be specifically describedbelow as the radiographic inspection apparatus.

The X-ray inspection apparatus comprises, as shown in FIG. 1, a holder 1which holds a circuit forming device K serving as an inspected objectsuch that the holder 1 rotates 360° about the axis intersecting thedirection of X-ray irradiation at right angles, an X-ray irradiator (anexample of an irradiation device) 2 for irradiating the circuit formingdevice held by the holder 1 with X-rays, an X-ray detector (an exampleof a radiation detector) 3 which is placed on a position correspondingto the X-ray irradiator 2 and detects X-rays passing through the circuitforming device held by the holder 1, a rotation control section (anexample of a rotation controller) 4 for rotating (rotating and moving)the holder 1 every predetermined degrees of angle based on predeterminedinspection data, an X-ray control section (an example of a radiationcontroller, also referred to as a radiation control section) 5 forinstructing the X-ray irradiator 2 to generate X-rays, a data storagesection (an example of a data storage device) 6 which is memory forstoring data on penetrated X-rays, the X-rays being detected by theX-ray detector 3, a tomogram creating section (an example of a tomogramcreating device) 7 for creating a plurality of tomograms from the dataon penetrated X-rays stored in the data storage section, an inspectiontarget extracting section (an example of an inspection target extractor)8 which receives the a plurality of tomograms created by the tomogramcreating section 7, specifies a range of tomograms to be inspected, andextracts the range, a projected image creating section (an example of aprojected image creator) 9 for creating projected images in a pluralityof directions, for example, three intersecting directions (thedirections of X, Y and Z axes) from the range (part) extracted by theinspection target extracting section 8, that is, projected images on theXY plane, YZ plane, and ZX plane, a defect detection section (an exampleof a defect detector) 10 for detecting a defect of the circuit formingdevice based on the plurality of (three) projected images created by theprojected image creating section 9, a control instructing section (anexample of a control instructing device) 11 for outputting instructionsignals to the constituent members 3 to 10 based on the predeterminedinspection data (for example, X-ray intensity, angle data on therotation of the holder, and so on), and an output device 12 such as amonitor which receives data on defects detected by the defect detectionsection 10 and displays the data in a predetermined display format. Atleast the tomogram creating section 7, the inspection target extractingsection 8, the projected image creating section 9, the defect detectionsection 10, and the control instructing section 11 are implemented byprograms (also acting as an arithmetic section) installed in a computeror implemented by devices with specialized functions.

The holder 1 is rotated every predetermined degrees of angle, forexample, every two degrees or three degrees (the angle is not limited)while holding the circuit forming device K. To be specific, the holder 1comprises a holding table (for example, the XY stage movable in twoaxial directions intersecting at right angles) 14 which is supported ina support frame so as to rotate about a predetermined axis (for example,horizontal axis) 13 and holds the circuit forming device K, and a motor15 for rotating the holding table 14.

The X-ray irradiator 2 generates X-rays by colliding acceleratedthermoelectrons with a target made of a predetermined material, andemits the X-rays. For example, any one of the following methods can beused: sealed tube method by which the inside is sealed almost in avacuum all the time, and open tube method by which a filament forgenerating thermoelectrons can be replaced and the inside needs to beevacuated in each use of the filament. However, in order to increase anenlargement ratio and a resolution, it is desirable to minimize thefocal size of an X-ray source, and thus in this device, open tube methodis used with a focal diameter of 1 μm.

The X-ray detector 3 has the function of converting the dose of X-raysto an electric signal and uses an X-ray flat panel in which lightconverted by a scintillator, which converts X-rays to visible light, isdirectly incident on an optoelectronic transducer such as a CCD and aCMOS and converted to an electric signal. As with an X-ray imageintensifier, after X-rays are converted by a scintillator which convertsX-rays to charged particles, a magnetic field may be controlled toconcentrate the charged particles, the charged particles may be collidedwith the scintillator and converted to visible light, and then the lightmay be converted to an electric signal by using an optoelectronictransducer such as a CCD and a CMOS.

Referring to the flowchart of FIG. 2, the following will discuss anX-ray inspection method of the circuit forming device.

First, the circuit forming device K to be inspected is held by theholder 1 in a predetermined position. And then, in response to aninstruction from the control instructing section 11, the holder land theX-ray irradiator 2 are operated via the rotation control section 4 andthe X-ray control section 5, and the X-ray detector 3 is simultaneouslyoperated.

In other words, the holder 1 which holds the circuit forming device K isrotated, for example, every two degrees or three degrees through 360° bythe rotation control section 4, and X-rays are emitted on each rotationstop position (moving position) (an example of an irradiation step, alsoreferred to as an X-ray irradiation step). As a matter of course, thecontrol instructing section 11 provides the X-ray control section 5 withan instruction on predetermined voltage and current, so that X-rays witha predetermined intensity are outputted from the X-ray irradiator 2.

And then, an instruction for the rotation of the rotating shaft of theholder 1 is outputted to the rotation control section 4 and the holder 1is stopped every two degrees. In synchronization with the stop, anirradiation signal is outputted to the X-ray irradiator 2 and an X-raydetection signal is outputted to the X-ray detector 3 (an example of aradiation detection step, also referred to as an X-ray detection step).

When the circuit forming device K is rotated 360° (one rotation) by theholder 1 and X-ray irradiation on the circuit forming device K iscompleted, 360 pieces of data on penetrated X-rays are detected by theX-ray detector 3 and stored in the data storage section 6 (data storingstep).

Subsequently, the data on penetrated X-rays on all the irradiationpositions (moving positions) in the data storage section 6 is inputtedto the tomogram creating section 7, and a number of tomograms of theoverall circuit forming device are created in a predetermined direction,for example, a number of horizontal tomograms are created (reconstructedby data processing) from the data on penetrated X-rays on all theirradiation positions (tomogram creating step). In other words, a numberof images are created by horizontally slicing the overall circuitforming device at predetermined vertical intervals.

For example, as shown in FIG. 3A, in the case of an inspection of ajoint where a component package 23 is mounted on a printed board 21 viaa spherical bump (BGA) 22 of solder or the like, that is, in the case ofan inspection of the spherical bump 22, a number of horizontal tomograms(also referred to as sliced images) A are created vertically as shown inFIG. 3B. FIGS. 3A and 3B show that a needle-like crack (an example of adefect) 24 appears diagonally in the joint (spherical bump) 22.

Subsequently, the horizontal tomograms A created by the tomogramcreating section 7 are inputted to the inspection target extractingsection 8. In the inspection target extracting section 8, an inspectionrange is specified and the external shape of the inspection range andthe crack 24 in the inspection range are extracted (defect extractionstep)

For example, when specifying the joint 22, both end positions facingeach other are specified to determine a range in the cross section. Tobe specific, as shown in FIG. 3A, coordinate a on an upper end andcoordinate b on the lower other end are specified.

And then, by pattern matching between the external shapes of thehorizontal tomograms A of the specified joint 22 and the previouslyknown circular external shapes of the spherical bump, the centerposition, radius, and so on are determined and extracted (instead ofpattern matching, binarization and edge detection may be used). Imagedata (for example, data on lightness) inside the external shape of theextracted joint 22 is compared with a predetermined threshold value andonly smaller values than the predetermined threshold value, for example,are extracted (larger values than the predetermined threshold value maybe extracted for some kinds of image data) Thus, the external shape ofthe joint 22 and the crack 24 are extracted.

Subsequently, data on the external shape and crack 24 extracted by theinspection target extracting section 8 is inputted to the projectedimage creating section 9. In the projected image creating section 9, thedata is added (also referred to as projected addition) along the X, Yand Z axes (three axial directions), so that three projected imagesshown in FIGS. 4A to 4C are created (projected image creating step).

Subsequently, the three projected images created by the projected imagecreating section 9 are inputted to the defect detection section 10 andbinarized based on a predetermined threshold value to clarify the crack24, and the region of the crack 24 is numbered, so that the position andsize of the crack 24 are detected (defect detecting step). Finally, theposition of the defect is determined among the three projected imagesand the result is displayed on the screen of the output device 12 suchas a monitor (defect output step).

The above explanation described the inspection of the single circuitforming device K. When a plurality of circuit forming bodies K (forexample, nine circuit forming bodies K in three columns and three rowson the holding table) are inspected at a time, the projected images ofall the circuit forming bodies K can be displayed at a time while beingdisplaced with respect to each other as shown in FIG. 5.

According to the foregoing radiographic inspection apparatus andradiographic inspection method, a circuit forming device to be inspectedis moved every predetermined degrees of angle to make a rotation, aplurality of tomograms are created using data on X-rays emitted andpenetrated on each rotation stop position, external shapes and defectsare extracted by performing data processing such as pattern matching andthreshold processing on the tomograms, projected images in threedirections intersecting at right angles are created using image dataindicating the extracted defects, and the defects are detected based onthe projected images. Thus even a long defect such as a crack can beeasily and positively detected in any direction based on the pluralityof projected images. According to the conventional method, in the caseof a small defect in a tomogram intersecting the irradiation directionof X-rays at right angles, the defect cannot be easily detected.

According to the radiographic inspection apparatus and the radiographicinspection method, a defect can be detected in a shorter time ascompared with detection on each tomogram.

In the present embodiment, the radiation is X-rays but gamma rays,neutron rays, and so on may be used. In this case, as a matter ofcourse, a gamma-ray or neutron-ray irradiator, a gamma-ray orneutron-ray detector, and a gamma-ray or neutron-ray control section areused as the irradiation device, the radiation detector, and theradiation control section of the present embodiment.

Further, in the present embodiment, when a projected image is created,an external shape is extracted by pattern matching, image data insidethe external shape is binarized according to a threshold value, and anaddition is performed in a projected manner to create projection data.When a projected image is created, a standard deviation and thedistribution among data of interest to be projected may be used asprojection data, instead of the data binarized according to thethreshold value. Thus even when target data is entirely changed, it ispossible to obtain projection data not being affected by the change.

Before a projected image is created, Laplacian filtering may beperformed on image data inside an external shape in order to enhance adefect and then subsequent processing may be performed.

In the present embodiment, a plurality of tomograms are created byrotating the circuit forming device about the axis intersecting theirradiation direction at right angles. For example, the circuit formingdevice may be rotated every predetermined degrees of angle (for example,1 degree or 2 degrees) in a state in which the normal of the circuitforming device (a normal to a substrate surface) is tilted with respectto an axis placed in parallel with the irradiation direction. In otherwords, the holder may cause the normal of the circuit forming device toswing (so-called precession) relative to the axis placed in parallelwith the irradiation direction.

Referring to FIGS. 6 and 7, the specific configuration of this case willbe discussed below.

In this case, a holder (also referred to as a swinging device) 31comprises a rectangular holding table (for example, an XY stage movablein two axial directions intersecting at right angles) 32 on which thecircuit forming device K is placed, a rectangle inner frame 34 whichholds the holding table 32 rotatably about a first axis (for example,the X axis) 33, a rectangular outer frame 36 which holds the inner frame34 rotatably about a second axis (for example, the Y axis) 35intersecting the first axis at right angles, a first motor 37 which isprovided on the inner frame 34 to rock the holding table 32 about thefirst axis 33, and a second motor 38 which is provided on the outerframe 36 to rock the inner frame 34 about the second axis. The motors 37and 38 are controlled in response to an instruction from the controlinstructing section 11 through a swinging control section 39.

To be specific, in response to an instruction from the controlinstructing section 11, the motors 37 and 38 are controlled through theswinging control section 39 such that as shown in FIG. 7, the holdingtable 32 swings at a predetermined angle a with respect to a third axis(for example, the Z axis) 40 intersecting the first axis 33 and thesecond axis 35 at right angles. In this state, photographing isperformed using radiation.

Although a defect is detected from the three projected images in thisembodiment, two projected images intersecting at right angles may beused to detect a linear defect. A linear defect affects more than apoint-like defect, and the creation of two projected images results inshorter image processing time than the creation of three images.

1. A radiographic inspection apparatus which irradiates an object toinspect an inside of the object, the radiographic inspection apparatuscomprising: a holder which rotates the object a predetermined angleabout an axis that intersects an irradiation direction at right anglesor swings the object a predetermined angle about an axis that isparallel to the irradiation direction; an irradiation device whichirradiates the object; a radiation detector which detects radiation thatpenetrates the object; a data storage device which stores data onradiation detected by the radiation detector; a tomogram creating devicewhich creates a plurality of tomograms based on the radiation datastored in the data storage device; a projected image creator whichcreates projected images in a plurality of directions based on theplurality of tomograms; and a defect detector which detects a defect inthe object based on the plurality of projected images.
 2. Theradiographic inspection apparatus according to claim 1, wherein theprojected images created by the projected image creator are for aplurality of projected planes intersecting at right angles.
 3. Theradiographic inspection apparatus according to claim 1, wherein theprojected image creator creates projected images by setting a thresholdvalue for the tomograms to extract therefrom parts corresponding to thedefect and adding the parts corresponding to the defect extracted basedon the threshold value.
 4. The radiographic inspection apparatusaccording to claim 1, wherein the radiation is one of an X-ray, a gammaray, and a neutron ray.
 5. A radiographic inspection method to irradiatean object to inspect an inside of the object, the radiographicinspection method comprising: irradiating the object and detecting aradiation that penetrates the object, which is rotated a predeterminedangle about an axis that intersects an irradiation direction at rightangles, or the object is swung a predetermined angle about an axis thatis parallel to the irradiation direction, creating a plurality oftomograms based on data from radiation that has penetrated an object,creating projected images in a plurality of directions based on theplurality of said tomograms, and detecting a defect of the object basedon the plurality of projected images.
 6. The radiographic inspectionmethod according to claim 5, wherein the radiation is one of an X-ray, agamma ray, and a neutron ray.
 7. The radiographic inspection methodaccording to claim 5, wherein the projected images created by theprojected image creator are for a plurality of projected planesintersecting at right angles.
 8. The radiographic inspection methodaccording to claim 5, wherein the projected image creator createsprojected images by setting a threshold value for the tomograms toextract therefrom parts corresponding to the defect and adding the partscorresponding to the defect extracted based on the threshold value.